example_synth: hardware mapping

Filling out the hardware mapping sections, and actually highlighting the changes in schematics instead of just the memory block.
Also includes Part 4 of the coarse-grain rep, looking at `memory_collect` and putting the `synth_ice40 -top fifo -run :map_ram` command in its own (sub)section.
Includes a `no_rw_check` section label in `memory.rst` for reference (because I can't remember how to reference by heading).

Not sure about the opt output after map_ram section which has an open TODO, and the final steps section is also still open.

docs/source/using_yosys/synthesis/memory.rst

@@ -253,6 +253,8 @@ Synchronous SDP read first
 			read_data <= mem[read_addr];
 	end
 
+.. _no_rw_check:
+
 Synchronous SDP with undefined collision behavior
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~